When two or more audio devices play at the same time, there may be an echo effect that reduces the enjoyment of the sound by the listener. These audio devices may be cabled to a controller device which provides the audio data to them. A bus may be used to supply this data. Alternatively, the different devices may communicate with each other through wireless communication, such as through an RF or infrared port.
In a system in which one computer or device broadcasts a single digital audio stream that is then simultaneously received by more than one receiving device, the different receiving devices will often play their audio slightly out of sync with each other, due to differing latencies in receiving and processing the digital audio stream. This produces an echo or delay effect which causes a listener to receive the same audio at slightly different times from the multiple devices. An additional echo effect may arise from a difference in distance from the listener to the various receiving devices. The listener's enjoyment is impaired.
Prior devices have used clock synchronized receiving devices. In one prior device, a transmitting device inserted control track pulses into the digital audio stream at known intervals. Each receiving device obtained the time of the received track pulse and then delayed the playback of the audio stream until the received pulse was aligned with the next pulse at the known interval. In another prior device, the transmitting device transmitted to each receiving device a waveform sample, the playback time of the sample, and the latency value of the receiving device. Each receiving device then delayed the playback of the audio stream until the waveform sample was aligned with the received playback time of the sample.
None of the prior devices used audio patterns and a microphone for obtaining feedback as part of the synchronization method. Furthermore, these prior devices required clock synchronization of the transmitting device and/or the playback devices. Clock synchronization tends to increase circuit complexity, and thereby increase costs.
A method and apparatus for synchronizing the playback of audio from two or more devices is needed which does not require clock synchronization.